Evidence that dopaminergic axons provide a dense innervation of specific neuronal subpopulations in the rat basolateral amygdala.

Dopaminergic inputs from the ventral tegmental area and substantia nigra are involved in numerous emotional and behavioral functions mediated by the amygdala. Previous studies have shown that some dopaminergic axons selectively innervate subpopulations of neurons in the rat basolateral amygdala by forming dense pericellular arrays (baskets) that envelope the perikarya of these neurons. Because of the obvious functional significance of this innervation, a sequential two-color immunoperoxidase technique was used in the present study to determine which neuronal subpopulations are targeted. Pericellular baskets were seen in sections stained for tyrosine hydroxylase, but not for dopamine-beta-hydroxylase, suggesting that these axonal arrays are dopaminergic. Most baskets enveloped small ovoid or piriform perikarya, although a few in the anteroventral part of the basolateral nucleus were associated with larger pyramidal cells. Double-labeling immunohistochemistry revealed that all of the smaller baskets enveloped a subpopulation of parvalbumin-immunoreactive nonpyramidal neurons, but not nonpyramidal neurons containing vasoactive intestinal polypeptide or neuropeptide Y. Since these parvalbumin containing neurons are known to be GABAergic interneurons, the results of this study suggest that the actions of dopamine in the basolateral amygdala are mediated, in part, by a subpopulation of inhibitory interneurons.

Synaptology of prefrontal cortical projections to the basolateral amygdala: an electron microscopic study in the rat.

Prefrontal projections to the magnocellular basal amygdaloid nucleus (Bmg) of the rat were investigated using Phaseolus vulgaris leucoagglutinin (PHA-L) as an anterograde tracer. Electron microscopic examination revealed that most axon terminals in Bmg labeled by PHA-L injections into the prelimbic area contained round synaptic vesicles and made asymmetric synapses. The great majority of labeled terminals (93%) made synaptic contact with dendritic spines; a few contacts (7%) were seen with thin dendrites. These findings indicate that the main postsynaptic targets of PFC afferents to Bmg are spiny pyramidal neurons, the projection neurons of the basolateral amygdala. The morphology of the synapses suggests that they are excitatory.

Biocytin injections produce selective neuronal labeling in the rat CNS.

Large injections of biocytin into the lateral ventricle or brain resulted in the labeling of particular neuronal subpopulations in the rat CNS. Localization was accomplished using the avidin-biotin-peroxidase technique. In many cases the staining of neurons was totally complete and resembled that obtained with the Golgi technique. Regions containing labeled cells included the olfactory bulb, cerebral cortex, hippocampus, amygdala, striatum, hypothalamus, superior and inferior colliculi, cerebellar cortex, and dorsal horn of the spinal cord. Only particular cell types were labeled in each of these regions. The results of this study suggest that there is selective uptake and/or retention of biocytin, or a biotinylated metabolite of biocytin, by subpopulations of CNS neurons.